Prior hydroenhancement technology teaches that certain properties of woven or knitted fabrics, such as cover, yarn blooming, surface texture, hand, drape, etc., can be enhanced by impacting the surface of the fabric with rows of jet streams from a series of overhead manifolds as the fabric is conveyed on a support surface, as illustrated in FIG. 2, for example. Such conventional hydroenhancing equipment is described in greater detail in commonly-owned U.S. Pat. No. 4,967,456 of Sternlieb et al., issued on Nov. 6, 1990, entitled "Apparatus and Method For Hydroenhancing Fabric", which is incorporated herein by reference.
Generally, the conventional view has been that the degree of enhancement is related to the amount of energy imparted to the fabric. That is, the more energy delivered to the fabric, the more pronounced the enhancement effect. For example, U.S. Pat. No. 3,493,462 to Bunting teaches that the degree of surface treatment is related to the total energy E expended per weight of fabric in a pass under a hydrojet manifold, as calculated by the following equation:
E=0.125 (YPG/sb), in hp.-hr./lb. of fabric, where
Y=number of hydrojets (orifices) per linear inch of manifold, PA0 P=pressure of fluid in the manifold, in p.s.i.g., PA0 G=volumetric flow of fluid in cu.ft./min. per orifice, PA0 s=speed of passage of fabric under the manifold, in ft./min., and PA0 b=weight of fabric treated, in oz./sq.yd.
This equation provided by Bunting is a standard calculation used in the industry for energy expended in the hydrotreatment of a fabric.
The degree of enhancement imparted to the surface of a fabric can be measured in terms of the cover of the fibers in the fabric. Cover has an inverse relation to the air permeability of the fabric, which is measured in cu.ft./min./sq.ft. (cfm/ft.sup.2) . The graph in FIG. 1 illustrates the relationship, as known conventionally, between the amount of energy expended in hydrotreatment and the resulting air permeability property of the treated fabric. The graph shows that as the amount of energy expended (in hp-hr/lb) with each pass increases, the degree of enhancement, i.e., the cover of the fabric increases and, conversely, air permeability (in cfm/ft.sup.2) decreases.
Conventional equipment for hydroenhancing fabric has employed high-speed processing lines having one or more manifolds in parallel across the width of fabric conveyed in a machine direction on a conveyor. Conventional techniques for obtaining suitable hydroenhancement of fabric include using high pressures of fluid jetted from the manifold, large-diameter jet orifices or lowered processing speeds to impact high energies of fluid per area of fabric per unit of time, and/or multiple manifold configurations. However, the requirements for handling high fluid pressures or fluid energies or multiple manifolds can increase the equipment size and complexity, as well as equipment and maintenance costs, significantly. The use of high total delivered energies, say in the range of 1.0 or 2.0 hp-hr/lb, is also less efficient, as improvements in fabric enhancement tend to taper off with further increases in energy. The use of high delivered energies can also cause greater fabric shrinkage, and can exacerbate the problem of interference patterns generated on the surface of the fabric by the impacting jet streams in relation to the yarn spacing in the fabric.
It is therefore a principal object of the present invention to improve the efficiency of fabric hydroenhancement by obtaining better fabric cover properties while decreasing the total energy expended in hydroenhancing. It is a further object of the invention to obtain improved fabric hydroenhancement while reducing the amount of fabric shrinkage due to enhancement. Another object of the invention is to reduce or eliminate the generation of interference patterns in hydroenhanced fabric. A further object is to provide improved equipment for fabric hydroenhancing that obtains these stated purposes.